[Bug web/61054] Clearly note effect of memcpy optimization improvements in 4.9 changes

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61054

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
We already documented it, see "null pointer checks optimized away more
aggressively" at http://gcc.gnu.org/gcc-4.9/porting_to.html